Method of treating cement clinker

ABSTRACT

A method of treating cement clinker by grinding the clinker in a tubular mill while charging water, gypsum, and, optionally, also a water-reduction agent to the mill at the same time. The water has a pH of from about 9 to about 13. A microfill agent and/or a water-reduction agent is mixed with said the high pH-value water to form a slurry, which is added to the clinker during the grinding process together with microfill agent and/or water-reduction agent in a dry state. The high pH value of the water can be obtained by electrolysis.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a method of treating cement clinker andmore specifically to a method of treating cement clinker in the processof grinding the same.

2. Description of the Related Art

The cement clinker to which the invention relates is preferably Portlandcement clinker, although it is not restricted to Portland cementclinker, but can be applied with other cement clinkers.

The nearest prior art is described in European Patent Application EP 0081 861 and in Publication WO 94/00403, which teach methods of grindingPortland cement clinker with mineral additives and an organic waterreduction agent. According to the last-mentioned publication, water isalso added to the last mill chamber with the intention of adjustingtemperature.

As a result of the physical and chemical adsorption of molecules ofwater-reduction agent on the clinker particles, the resultant groundcement will have a reduced water requirement and also greater strengthin comparison with standard Portland cement. One decisive drawback withthis method is the difficulty in controlling the extent of the reactionbetween Portland clinker and water reduction agent, this reaction havinga direct influence on the instability of the properties of the finalcement.

The same reduction in water requirement can also be achieved by adding awater reduction agent directly to concrete with water, in accordancewith conventional methods. No appreciable increase in the chemicalreactivity of Portland clinker can be achieved with these methods.

SUMMARY OF THE INVENTION

The present invention relates to a method of treating cement clinkerwhilst grinding the clinker and adding different substances thereto, inorder to enhance the strength properties of the cement produced.

The present invention thus relates to a method of treating cementclinker, by grinding the clinker in a tubular mill whilst adding waterand gypsum and possibly also a water reduction agent, wherein the methodis characterized by injecting water that has a pH of approximately 9-13into the mill during grinding of the clinkers.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The invention will now be described in more detail with reference tovarious embodiments thereof.

Cement clinker is normally processed by first heating the clinker orcalcine in a kiln at a temperature of 900-1450° C., such as to form thecompounds 3 CaO SiO₂, 2 CaO SiO₂, 3 CaO Al₂O₃ and 4 CaO Al₂O₃ SiO₂. Thistreatment process results in normal Portland cement.

In a second stage, the clinker is ground together with gypsum toparticle sizes of between 10-20 micrometers, in a tubular mill thatincludes steel balls. Water is added during this grinding process. Thepresent invention relates to this second stage.

According to the present invention, the water has a pH of about 9-13 andis injected into the mill during grinding of the clinkers.

According to one very preferred embodiment of the invention, the waterinjected has been brought to this pH-value by means of electrolysis.

OH⁻-ions are thus injected into the mill. These ions constitute highlyreactive radicals that fasten to the surfaces of the non-hydrated cementparticles, and facilitate formation of the complex qCaO.mSiO₂.nH₂O. Thiscomplex is formed on the surfaces of the cement particles.

Grinding of the clinker in the tubular mill will thus result in a dryproduct that contains cement particles which have a diameter of 10-20micrometers, these particles being prehydrated insomuch that theirsurfaces are covered, either completely or partially, with a prehydratedcoating that includes said complex.

Because the particles are prehydrated, they are very reactive.Adsorption of OH⁻-radicals on the surfaces of the clinker particlesresults in said complex-building and activation by virtue of theformation of a film of hydrosilicates on the particles. This complexacts as a nucleant for subsequent reaction with water. In combination,this results in a significant improvement in the strength development ofcement paste and a reduced porosity, as will be evident from thefollowing examples.

According to one preferred embodiment, a microfill agent and/or awater-reduction agent is/are added during the grinding process.

According to one highly preferred embodiment of the invention, part ofthe microfill agent and/or the water-reduction agent are mixed with saidwater of high pH-value to form a slurry which is injected into the millduring the grinding process, while adding dry microfill agent and/orwater-reduction agent during the grinding process.

It is preferred that the water-reduction agent is slurried and that thisslurry is brought to said pH-value by electrolysis, prior to injectingthe slurry into the mill.

The ratio between the dry substance/substances and the slurry willpreferably lie in a range of between 95 weight %/5 weight % to 85 weight%/15 weight %.

The liquid phase of the slurry will preferably exceed 50% of the weightof the slurry.

According to another preferred embodiment, microfill agent in the formof SiO₂-containing substances, such as blast furnace slag and limestone,are delivered to the tubular mill in a quantity of up to 80% of thecombined weight of microfill agent, water-reduction agent and waterdelivered to the mill.

According to another preferred embodiment, water-reduction agent in theform of polymers, such as lignosulfonate-based polymers that containnaphthalene or melamine or combinations thereof, are delivered to thetubular mill in an amount of up to 5% of the combined weight ofmicrofill agent, water-reduction agent and water delivered to the mill.

A number of examples will now be described. The Table that follows theexamples sets forth the results obtained with respect to waterrequirement, compression strength and porosity.

EXAMPLE 1

Portland cement clinker having the chemical composition in weight %C₃S=64.5, C₂S=11.0, C₃A=9.5, C₄AF=9.0, Na₂O=0.10 and K₂O=0.25 wascharged to a tubular mill. The letter C in this composition is anabbreviation of CaO, A is an abbreviation of Al₂O₃ and F is anabbreviation of Fe₂O₃. The tubular mill measured 1.5 m in diameter and3.5 m in length. Gypsum was charged together with the Portland cementclinker in an amount corresponding to 3% of the weight of the clinker,together with non-distilled water taken from the normal water supplysystem. This water had been subjected to electrolysis in a directcurrent field having an amperage of 1.75 A/dm² and a voltage of 380 Vfor two minutes, so as to obtain a pH-value of 11.2. The water wasdelivered to the tubular mill in a dispersed form. The cement producedhad a specific surface area (Blaine) of 4800 cm²/g.

The cement thus obtained was mixed with water in a Hobart mixer forthree minutes, to obtain a cement paste of standard consistency. Thecement paste was poured into a cubic steel mould having sides 20 mm inheight, and compacted on a vibration table. The cement paste sample wascured in water at 20° C. and then subjected to compression tests.

EXAMPLE 2

A Portland cement clinker according to that described in Example 1 wasground in a traditional manner and a cement paste sample was produced inaccordance with Example 1 above.

EXAMPLE 3

A Portland cement clinker corresponding to the clinker defined inExample 1 was ground in accordance with Example 1 together withpre-ground limestone as a microfill agent, said limestone having aspecific surface area (Blaine) of 3000 cm²/g. The total weight of thepre-ground limestone corresponded to 15 weight % of the weight of thecement and was charged in two different states, namely 80% in a solid,dry state and 20% in a state slurried with 35% water.

The liquid phase of the slurry comprised tap water that had beenelectrolyzed with 3.5 A/dm² and 380 V over a period of two minutes, toobtain a pH of 11.5.

The slurry was charged to the tubular mill in a dispersed state. Theslurry was charged to the mill together with clinker, gypsum and the drymicrofill agent. The cement produced had a specific surface area(Blaine) of 4780 cm²/g.

Cement paste samples were produced in the manner described in Example 1.

EXAMPLE 4

Portland cement clinker and a limestone microfill were groundtraditionally in the same quantities as those in Example 3, with solelythe microfill being added in a dry state. The cement produced had aspecific surface area (Blaine) of 4813 cm²/g.

Cement paste samples were produced in the manner described in Example 1.

EXAMPLE 5

The procedure followed in this example was the same as that used inExample 1, but with the exception that in this case a liquidizing agentwas added to the system. The liquidizing agent was in the form of a40%-solution of a melamine type superplasticizing agent, namely Flyt 92®produced by Cementa AB, Sweden. The liquidizing agent was added in anamount corresponding to one weight % of the total mill charge.

The liquidizing agent was added to the liquid phase of the slurry priorto subjecting the same to electrolysis.

Cement paste samples were produced in accordance with FIG. 1.

EXAMPLE 6

The procedure followed in this example was the same as that used inExample 2, i.e. traditional grinding, but with the exception that theliquidizing agent according to Example 5 was added with water in aconventional manner in the same quantity as that in Example 5, duringcasting of the cement paste.

Cement paste samples were produced in the manner described in Example 1.

EXAMPLE 7

The procedure followed in this example was the same as that followed inExample 1. The cement paste obtained was then treated in accordance withthe method described in International Patent Publication No. WO94/25411(PCT/SE94/00389), wherein the cement paste was treated in a vibratorymill having a vibration circle of 10 mm in diameter and operating at afrequency of 110 r.p.m., over a period of thirty minutes. The weightratio of grinding media to mixture was 9:1.

Cement paste samples were produced in accordance with Example 1.

EXAMPLE 8

The procedure followed in this example was the same as that followed inExample 2. The cement paste obtained was then treated in accordance withthe method described in International Patent Publication No. WO94/25411(PCT/SE94/00389); see Example 7 above.

TABLE The “required water quantity” column in the Table denotes theamount of water that is required to produce a cement paste of standardconsistency in percentage of the cement weight. Compression Requiredstrength, Mpa water quan- Curing Time Days Porosity Example tity (%) 1 728 cm³/g 1 23.5 35.1 73.6 91.1 0.070 2 23.4 24.4 57.4 68.8 0.091 3 23.230.2 68.2 75.1 0.079 4 23.5 18.9 44.4 54.9 0.092 5 19.8 48.2 87.1 100.30.034 6 20.1 39.1 70.3 82.1 0.041 7 23.1 39.7 80.1 98.0 0.066 8 23.536.3 74.1 92.0 0.069

As is evident from the above Table, the cement paste produced inaccordance with the inventive method has a greater mechanical strengthand a reduced priority. The water requirement, however, is roughly thesame.

It will therefore be evident that the present invention provides aPortland cement of considerably higher chemical reactivity than that ofnormal Portland cement, which is reflected in the fact that the cementpaste cures more quickly at a given strength and obtains a significantlyhigher final strength.

Although the invention has been described above with reference tovarious examples and also with reference to various embodiments, it willbe understood by the person skilled in this art that the aforesaidratios relating to the compounds used can be modified with the aid ofappropriate tests such as to obtain a cement that has the propertiesdesired.

The aforesaid embodiments do not therefore restrict the scope of thepresent invention, since variations can be made within the scope of thefollowing claims.

What is claimed is:
 1. A method of treating cement clinker, said methodcomprising the steps of: providing cement clinker, and grinding saidclinker in a tubular mill while adding water and gypsum, wherein thewater added during grinding of the clinker has a pH of from about 9 toabout
 13. 2. A method according to claim 1, including the step ofelectrolyzing the water before addition to the mill to provide saidwater pH-value.
 3. A method according to claim 1, including the step ofadding during the grinding step an agent selected from the groupconsisting of microfill agents, water-reduction agents, and mixturesthereof.
 4. A method according to claim 3, including the step of forminga slurry by mixing a part of an agent selected from the group consistingof microfill agents, water-reduction agents, and mixtures thereof withsaid water having said pH-value, and injecting the slurry into the millduring the grinding step together with a component in a dry state andselected from the group consisting of microfill agents. water-reductionagents, and mixtures thereof.
 5. A method according to claim 4, whereinthe ratio of dry component to slurry is between about 95 weight %: 5weight % and about 85 weight %: 15 weight %.
 6. A method according toclaim 4, wherein the slurry has a liquid phase that exceeds 50% of theweight of said slurry.
 7. A method according to claim 3, including thestep of adding to the mill an SiO₂-containing microfill agent in anamount corresponding to up to about 80% of the combined weight ofmicrofill agent, water-reduction agent and water.
 8. A method accordingto claim 3, including the step of adding to the mill apolymer-containing water-reduction agent in an amount corresponding toabout 5% of the combined weight of microfill agent, water-reductionagent and water.
 9. A method according to claim 8, including the step offorming a slurry containing the water-reduction agents and electrolyzingthe slurry to obtain said pH-value prior to adding the slurry into thetubular mill.
 10. A method of treating cement clinker, said methodcomprising the steps of: providing cement clinker, and grinding saidclinker in a tubular mill while adding water, gypsum and awater-reduction agent, wherein the water added during grinding of theclinker has a pH of from about 9 to about
 13. 11. A method according toclaim 10, including the step of electrolyzing the added water to providesaid water pH-value.
 12. A method according to claim 10, including thestep of adding during the grinding step an agent selected from the groupconsisting of microfill agents, water-reduction agents, and mixturesthereof.
 13. A method according to claim 12, including the step offorming a slurry by mixing a part of an agent selected from the groupconsisting of microfill agents, water-reduction agents, and mixturesthereof with said water having said pH-value, and injecting the slurryinto the mill during the grinding step together with a component in adry state and selected from the group consisting of microfill agents,water-reduction agents, and mixtures thereof.
 14. A method according toclaim 13, wherein the ratio of dry component to slurry is between about95 weight %: 5 weight % and about 85 weight %: 15 weight %.
 15. A methodaccording to claim 7, wherein the SiO₂-containing microfill agent isselected from the group consisting of blast furnace slag, limestone, andmixtures thereof.
 16. A method according to claim 8, wherein thepolymer-containing water reduction agent is a lignosulfate-based polymerincluding an additive selected from the group consisting of naphthalene,melamine, and combinations thereof.